Tanning preparation and process



Patented May 6, 1930 I UNITED STATES PATENT OFFICE RALPH W. PREY, OFMOUNT MARYLAND, ASSIGNOB TO THE AND'THE PEOPLE OF THE UNITED STATES OFAMERICA TANNING PREPARATION AND PROCESS 1110 Drawing. Originalapplication filed April 28, 1927, Serial 110. 187,418. Divided and thisapplication filed my a1, 1925.

Serial m5. 296,628.

7 (GRANTED man ran ACT or inner: a, 1883, asmammn nan. so, 192s; 870 o.e. m

This invention is made under the act approved April 30, 1928, and theinvention herem described, if patented, may be manufactured and used byor for the Government for governmental purposes without payment to me ofany royalty thereon. I hereby dedicate the invention herein described tothe free use of the public, to take effect upon the granting of a patentto me.

This application is a divisional application of my application forpatent which bears Serial No. 187,418, filed April 28, 1927, on

tanning preparations and processes.

According to my invention tanning preparations, in either liquid orsolid form, are produced from chromium and iron. These preparations canbe used for tanning with both the chromium salts and iron salts prescut,the two tanning principles acting either simultaneously or successively,or, if desired,

these preparations, without removal of the iron salts, can be used fortanning with the chromium salts only, producing a leather of normalchrome crust color and ofa better than normal substance, particularly inthe loose and more flabby parts of the hide or skin. The production ofsuch leather in the presence of relatively high percentage of iron saltsin a non-tanning state is also a novel feature of my invention.

While metallic chromium and metallic iron are available in severalforms, a particularly convenient and economical commercial source is thealloy known as ferro-chrome. Ferrochrome is readily available in largequantities. Its composition can be controlled to produce, from a rawmaterial standpoint, a

product of unusual phys'cal and chemical uniformity. It has a fu eradvantage for I tanning in that the chromium predominates over the iron.

Ferro-chrome alloys are divided into two classes, high-carbonferro-chrome and lowcarbon ferro-chrome. While either may beused,low-carbon ferro-chrome alloys are not to be preferred as they arerelatively higher priced and also are needlessly refined with respect tothe removal of carbon.

The percentage composition range for a good grade of high-carbonferro-chrome may be represented as follows:

Cr to Fe 0 to 30% C I 4to 6% Si and other constituents 1 to 2% It willthus be seen that ferro-chrome'is extremely rich in chromium and iron.

According to my invention chromium and iron are dissolved in water andhydrochloric acid in suitable proportions. Hydrochloric acid isparticularly advantageous under some conditions of tanning because thechlorides known neutralizing agents such as the oxides,

hydroxides, carbonates, borates, phosphates, and acetates of the alkalisand alkali-earths may be used, the selectionof the neutralizing agentdepending largely upon the desired properties 0 the leather.

After partial neutralization the solution is 7 ready for immediate useor it may be evaporated to dryness or other degree of concentration forstorage or shipment.

Simply as an illustration of the preparation of such a stock tanninsolution, but in no sense a restriction as to the kind and quantity ofmaterials, the following example is offered:

.Ewample 1.To one part by wei ht of ferro-chrome alloy add a mixture 0%from five to seven parts by weight of water and from five to six partsby weight of 20 'to 22 B. hydrochloric acid. After the reaction subsidesboil gently until the ferro-chrome is dissolved, keeping the originalvolume about constant, then determine the Fe, Cr, and titratable CI inthe solution.' From these data calculate the Cl equivalent to-the Fe asFeCl the O1 equivalent to the Or as 0101.,

and the free or excess Cl. Ignore the Cl of the FeCl and calculate thequantity of M200, necessary to neutralize all of the excess Cl and alsothat proportion of the Cl associated with the chromium to give the de- 5sired basicity or degree of neutralization.

The most suitable basicity must be determined for the particularconditions of use. Dissolve the required quantity of Na CO in water andadd it to the ferro-chrome solution slowly while stirring vigorously.The resulting solution is then ready for tanning.

In the tanning preparation such as described the chromium salts and ironsalts are in the reduced state, in which state the chromium tans whereasthe iron does not. As a consequence, and if desired, chrome tanning canbe carried on without any iron tanning. For such a process the hides orskills after coming out of the customary foretanning operations such asliming, unhairing, d g,

and pickling, are started in the tanning operation proper .with thestock iron-chromium solution in the same manner'thatan ordinary stockchrome solution is used,-the necessary as quantity of. stockiron-chromium solution being based on its (Jr- O; content and the wei htof the hides or skins. When the last hal of the taming o eration isreached a neutralizing a nt suc for example, as NaHCO. is so adde tojust short of the precipitation point of the liquor and the tanning iscontinued until the leather res onds properly to the boiling water test.it this sta e, or after horsin the leatheris washed ee of iron 88 salts.e remaining operations, including the final neutralization of theleather, are carried out in the usual manner.

By such a rocess a chrome tanned leather of a normal c rome crust coloris obtained 1n the presence of material quantities of iron salts in anon-tanning state. While the iron salts do not enter into the tanningand thus color the leather their presence in the liquor results in achrome tannedleather of more than the customary ass? or substanceespecially in'the naturally'flabbier parts of the hide or skin. i w

Iron-chromium preparations such as described can alsobe' used to carryon ajoint chrome-iron tannage with the roduction of leathers of uniqueand desirab e properties. For such. a joint tannage the iron in' thesolution is oxidized to the ferric or tanning state by suitable meanseither before the tanning operation proper is started or later on afterthe chrome tanning has beenpartially or en-.

. tirely completed.

Various oxidizing agents can be used. So-

dium dichromate has, however, several ad'- vantages in that theoxidation of the iron "is readily carried to completion at ordinary '5temperatures and the chromium reduced thereby from the dichromatebecomes avail,"

as additional tanning material. The re as able 'tity .the calculatedFeCl content of the ferroaction may be represented-by the followingwell-known equatlons:

As shown, the reaction reduces the acidity of the tanning liquor.Consequently in tanning a further neutralization of the liquor, which isoften practiced in ordinary mineral tanning, is not necessary. I

As an illustration of a procedure for a joint chromium-iron tannage thefollowing exam- I pleois ofiered.

Ewample .2.-Using a stock ferro-chrome alloy solution such as describedin Example 30 1, the first stages of the tanning operat on pro or arecarried out in the same manner as or ordina stock chrome solutions,except that the quantity of stock-ferro-chrome alloy solution to be usedas based on its Cr,O, 5

content and the weight of the hides or skins can beless than thecustomary quantity because of the subsequent tanning action of the ironpresent. ThlS lBdllCtlOIl may be from 15 to 25 per cent of the allowanceof 0&0, for ordinary stock chrome solutions. After all of the stockferro-chrome solution has been added and the tanning is about halfcompleted Na Cr Or2H O, dissolved in water, is slowly added with motionand while the tanning is bein continued. The required quanof Na &r,O{-2HO is determined from chrome solution used, by means of the oxidation-equation alreadygiven. The tanning is me then continued until thedesired degree of joint chromium-iron tannage is obtained, after whichthe-leather is washed, neutralize'd, and finished as is customary.

the leathers produced thereby are of excelthat is suitable for manypurposes, thus making unnecessary extra dyeing operations. The naturalcolor being mineral in nature and being all through the leather as wellas on its surfaces, is unusually permanent.

I claim p 1". The process of making a tanning .preparation whichconsists in dissolving chromium and iron in hydrochlori acid and waterai d rendering thenesultiug solution basic by the 125 I addition of anaIkaIi carbonate. 5

. 2. The process'o making atanning prepa ration whic con stsjindissolving an alloy of'chron'n 1 and firdrijinhydrochloric acid andwaterand' the resulting solu-' 1 Such a t'annage proceeds verysmoothlyand 105 tion basic by the addition of an alkali carbonate.

3. The process of making a tanning preparation which consists indissolving ferrochrome in hydrochloric acid and water and rendering theresulting solution basic by the addition of an alkali carbonate.

4. The process of making a tanning preparation which consists indissolving chromium and iron in hydrochloric acid and water, thenrendering the resulting solution basic by the addition of an alkalicarbonate, and oxidizing the iron salts present to the ferric state bythe addition of an alkali dichromate.

5. The process of making a tanning preparation which consists indissolving an alloy of chromium and iron in hydrochloric acid and water,then rendering the resulting solution basic by the addition of an alkalicarbonate, and oxidizing the ironsalts present to the ferric state bythe addition of an alkali dichromate.

6. The process of making a tanning preparation which consists indissolving ferrochrome in hydrochloric acidand water, then rendering theresulting solution basic by the addition of analkali carbonate, andoxidizing the iron salts present to the ferric state by the addition ofan alkali dichromate.

7. A chrome tanning preparation comprising a solution of chromium andiron in hydrohloric acid and water, which solution has been renderedbasic.

8. A chrome tanning preparation comprising a solution of ferro-chrome inhydrochloric acid and water, which solution has been rendered basic.

9. The step in the process of making chrome leather comprising thetanning of hides and skins with a solution of chromium and irondissolved in hydrochloric acid and water and rendered basic.

10. The step in the process of making chrome leather comprising thetanning of hides and skins with a solution of ferrochrome dissolved inhydrochloric acid and water and rendered basic.

11. The steps in the process of making chrome-iron leather comprisingthe tanning of hides and skins with a solution of chr0- mium and irondissolved in hydrochloric acid and water and rendered basic, followedduring the tanning by the addition to the solution of an oxidizing agentto oxidize the iron salts present to the ferric state.

12. The steps in the process of making chrome-iron leather comprisingthe tanning of hides and skins with a solution of ferrochrome dissolvedin hydrochloric acid and water and rendered basic, followed during thetanningby the addition to the solution of an oxidizing agent to oxidizethe iron salts present to the ferric state.

RALPH -W. FREY.

